1. Field of the Invention
This invention concerns a liquid crystal compound for use in liquid crystal devices and, particularly, it relates to a novel optically active (chiral) substance inducing twisted arrangement in liquid crystals.
2. Description of the Prior Art
As the operation principle for liquid crystal display devices, there have been known a twisted nematic (TN) system using a nematic liquid crystal phase, a phase transition system using a cholesteric liquid crystal phase and the like. In any of these systems, liquid crystal mixtures in which chiral substances are added with an aim of inducing the twisted arrangement in the liquid crystals have been used. Further, an attention has been attracted to a high speed light switching device by using smectic liquid crystals, particularly, a smectic C* (SmC*) liquid crystal phase having a feature in the twisted arrangement and utilizing the ferroelectric property thereof in recent years. In this device, a SmC* liquid crystal compound which is a chiral substance per se or a SmC* liquid crystal mixture incorporated with chiral substance have been used.
In this way, the chiral substance inducing the twisted arrangement is extremely important for liquid crystal display devices. However, it is necessary for the chiral substances used in liquid crystal display devices or the likes that not only they have rotatory power but it is also important that the substances per se are of liquid crystal property or the liquid crystal property is not reduced remarkable when they are added to the liquid crystal mixture. Any way, it is important that the liquid crystal property of the liquid crystal mixture is not lost when the substances added thereto.
However, there have been only few chiral substances that can completely satisfy the demands as described above.